SECT. 141.] THE TEETH. 30 



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The permanent teeth are developed exactly in the same manner 

 as the milk-teeth. Their ossification commences in the first large 

 molars some time before birth, proceeds in the first, second and 

 third year upon the incisors, canines and small molars, and, at 

 length, also involves the second large molars, so that in the sixth 

 or seventh year, forty-eight teeth are contained in the two jaws, 

 viz., twenty milk-teeth and all the permanent, except the wisdom 

 teeth. In the shedding of the teeth, the bony partitions, which 

 separate the alveoli of the permanent from those of the milk- 

 teeth, are absorbed, and at the same time the fangs of the latter 

 disappear from below upwards, in consequence of a process not 

 yet exactly understood. Thus the permanent teeth, whose roots 

 meanwhile elongate, come to lie directly under the loosened 

 crowns of the milk-teeth, which, on the further advancement of 

 their successors, fall out and give place to them. The eruption of 

 the permanent teeth takes place in the following order : first 

 large molar in the seventh year, central incisor in the eighth year, 

 lateral incisor in the ninth year, first bicuspid in the tenth, second 

 bicuspid in the eleventh year, canine tooth in the twelfth year, 

 second large molar in the thirteenth year, third molar or wisdom 

 tooth between the seventeenth and nineteenth years. 



The gum of the foetus, and especially of the newly-born infant, 

 is, before the eruption of the milk-teeth, whitish, very firm, and 

 almost of the consistence of cartilage, on which account, perhaps, 

 it has been also called gum-cartilage, although, in its structure, it 

 has not the slightest resemblance to cartilage, and consists of the 

 ordinary elements of the mucous membrane, with a considerable 

 intermixture of a more tendinous tissue. The bodies, the size of 

 a millet- seed, described in it by Serves, and which are said to be 

 glands which secrete tartar, the so-called glandules tartaricce, are 

 collections of epithelium, and probably of a pathological nature 

 (see my Micr. Anat. ii. 2, p. 92) . 



The tooth-sacs have an envelope of connective tissue with vessels and 

 nerves, from the floor of which the tooth-germ, pulpa dentis arises. This 

 corresponds in form to the future tooth, consisting of an inner part rich in 

 vessels, and subsequently also in nerves, and of an outer non-vascular pov- 

 tion. The latter is bounded by a delicate structureless membrane, the 

 membrana pnrformutiva (IJaschkow), which is of no significance in the forma- 

 tion of the tooth ; and beneath the membrane are cells 0-016'" to 0-024.'" 

 long, and 0-002'" to 0-004.5"' broad, with beautiful vesicular nuclei, and one 

 or more distinct nucleoli, which are placed close to one another, like an 

 epithelium upon the whole surface of the pulp ; they are not, however, so 

 sharply limited internally as an epithelium, and there is at least apparently 



